Elbow replacement apparatus and methods

ABSTRACT

Apparatus and methods for total elbow replacement are provided to allow a surgeon to intraoperatively select a linked or unlinked constraint by utilizing a connection located on the body of the ulnar and/or humeral stem. Additional modularity also allows the selection of a cemented or cementless stem as described herein. The modularity and adjustability provides a number of advantages.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 12/947,506, filed Nov. 16, 2010, which claims the benefit ofU.S. patent application Ser. No. 61/261,575, filed Nov. 16, 2009, eachof which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to prosthetic joints and moreparticularly, to an elbow implant system that has an articular surfacedesigned to gradually shift a contact point between components outwardlyas the joint undergoes varus/valgus rotation and further includes amodular construction to allow for the surgeon to select differentcomponents for use depending upon the particular application and/orobservations.

BACKGROUND

Joint arthroplasty is the most successful treatment thus far forrelieving pain and restoring function to patients suffering fromarthritis and other destructive joint problems. Hip and kneereplacements are quite common with more than half a million of eachprocedure performed annually in the US. The popularity of hip and kneearthroplasty has been established by the efficacy and durability ofthese types of joint replacements. For example, the Australian nationalregistry reports cumulative revision rates of only 4% at seven years forprimary total knee arthroplasty, while the Swedish national registryreports survivorships of greater than 93% at 10 years for hiparthroplasty. For total elbow replacement, the results are not as good,with the Norwegian Arthroplasty Register reporting a failure rate of 8%and 15% at 5- and 10-year follow up, respectively.

The two leading clinical indications for total elbow arthroplasty arerheumatoid arthritis and posttraumatic arthritis. The two primary elbowreplacement types used to treat these arthritic events are constrainedand unconstrained designs, also referred to as linked and unlinked,respectively. Linked elbow replacements have intrinsic stability as thehumeral and ulnar components are mechanically connected to one another,usually by a hinge. Some laxity exists to permit a small degree ofvarus-valgus and internal-external rotational movements. The humeral andulnar components in unlinked elbow replacements, however, are notmechanically connected. For these implants, the degree of varus-valgusand internal-external rotational movements are dependent primarily onthe quality of ligamentous and muscular integrity.

In the past, an unlinked elbow has been introduced with a porous coatingon the fixation surfaces of the humeral and ulnar components. However, astudy showed that of 32 elbow replacement arthroplasties in the testgroup (32 cementless humeral components, 4 cementless ulnar components),only one patient showed a radiolucent line around the humeral componentafter an average 3-year follow up. No radiolucent lines were exhibitedaround the ulnar components.

Currently, there are several devices for elbow replacement. TheCoonrad-Morrey total elbow arthroplasty (TEA) system employs linkedcomponents, including polyethylene bushings on the humeral and ulnarcomponents through which a metal axle passes, and an anterior flange onthe humeral component used in conjunction with bone graft to increasetorsional and anteroposterior stability in vivo. The humeral and ulnarcomponents are cemented into place. The hinge permits ±3.5° ofvarus-valgus motion, with the intent that the load will be transferredto the soft tissues before max angulation is achieved.

Recent studies have evaluated the success of the Coonrad-Morrey TEAs andin particular, one study evaluated 67 Coonrad-Morrey TEAs. Of these, 37were primary arthroplasties with a five-year survival rate of 72%. Theremaining 30 were revision arthroplasties, which had a five-yearsurvivorship of 64%. Other studies have reported ten-year survival of51% and fifteen-year survival of 24%. Clinical results have only rivaledhip and knee replacement in less active patients, such as those withrheumatoid arthritis. For this group, implant survivorship is about 90%at five to ten years.

An implant-related failure mode with the Coonrad-Morrey TEA is wear anddeformation of the polyethylene bushings, causing both decreasedfunction of the joint as the bushing-axle constraint decreases andosteolysis secondary to the release of large volumes of polyethylenewear particles. Studies have reported radiographic evidence of bushingwear in three of six patients after less than five years, requiringpatients to undergo revision surgery. Similarly, another study reportedbushing wear as the cause of failure in ten patients, all of whomrequired revision surgery an average of five years postoperatively. Astudy has shown that 1% of their patients required revision surgery foran isolated bushing exchange at an average of eight years after theirTEA. In yet another study, components retrieved from sixteen elbows infourteen patients were examined and found that damage to the humeral andulnar polyethylene bushings was nearly universal with asymmetricalthinning and elliptical plastic deformation. Metallic wear on thefixation stem of the ulnar component, consistent with loosening at theimplant-cement interface, was observed in most of the cases,underscoring the additional problem of aseptic loosening in TEAs.

The Discovery Elbow System from Biomet, Inc. is a linked, cemented totalelbow replacement. The hinge has an hourglass shape to maximizearticular surface contact between the humeral and ulnar components.Minimal bone resection maintains the integrity of the humeralepicondyles. The device preserves the ulnar collateral ligament.

The Latitude Total Elbow Prosthesis from Tornier is a modular, cementedtotal elbow replacement. This device is designed to restore the normalkinematics of the elbow joint creating a modular spool that allows thesurgeon to adjust the central, posterior, and anterior offset of thejoint axis. A second articular component can be attached to the ulnarcomponent to convert from unlined to linked. The device also has anoptional radial component. Limitations of using the Latitude include thecomplete dissection of the distal humerus that is required forimplantation of the components, the use of multiple jigs to locate thenatural joint axis that may not be present in a patient with rheumatoidarthritis, limited triceps split to gain access to the ulnar canal, andthe use of cemented components.

However, none of these devices allow for intraoperative adjustment ofsoft tissue tension. For the unlinked condition, conventional devices donot provide for mechanical constraint to varus/valgus motion. It wouldbe desirable to produce an elbow replacement with an articular surfacedesigned to gradually shift the contact point outwardly as morevarus/valgus motion is initiated, thus increasing the restoring momentat the joint. It would also be desirable to provide apparatus andmethods for total elbow replacement that allow a surgeon tointraoperatively select a linked or unlinked constraint, accommodatecemented or cementless fixation, as well as adjust soft tissue tensionof the joint.

SUMMARY

In accordance with the present invention, apparatus and methods fortotal elbow replacement are provided to allow a surgeon tointraoperatively select a linked or unlinked constraint by utilizing aconnection located on the body of the ulnar and/or humeral stem.Additional modularity also allows the selection of a cemented orcementless stem as described herein. The modularity and adjustabilityprovides a number of advantages.

In one embodiment, an elbow prosthesis includes a humeral stem componenthaving a distal end and a proximal end. The prosthesis also includes ahumeral condyle (condylar) component having a distal end and a proximalend, with the proximal end of the humeral condyle component beingadapted to attachably engage the distal end of the humeral stemcomponent. The distal end of the humeral condyle component includesdistally extending portions.

An ulnar stem component is provided and has a distal end and a proximalend. The ulnar stem component tapers from the proximal end to the distalend. The ulnar bearing component is adapted to attachably engage theproximal end of the ulnar stem component and the distally extendingportions of the humeral condyle component.

In another embodiment, an elbow prosthesis includes a humeral stemcomponent and an humeral condyle component associated with the humeralstem component. The humeral condyle component has distally extendingportions that define condyle bearing surfaces. The prosthesis alsoincludes an ulnar stem component and an ulnar bearing componentassociated with the ulnar stem component. The ulnar bearing componenthas bearing surfaces that receive and engage the distally extendingportions of the humeral condyle component. Each of the condyle bearingsurfaces and the bearing surfaces of the ulnar bearing component has across-section in a coronal plane that exhibits at least two differentradii such that varus or valgus rotation of the humeral condylecomponent relative to the ulnar bearing component causes a contact pointbetween the condyle bearing surface and the bearing surfaces of theulnar bearing component to move outwardly (laterally).

In another embodiment, an elbow prosthesis includes a humeral implanthaving a stem and a humeral condyle portion disposed at an end of thestem. The humeral condyle portion includes distally extending portions.The prosthesis also includes an ulnar stem component having a distal endand a proximal end. The ulnar stem component is tapered from theproximal end to the distal end. An ulnar bearing component that is aseparate component relative to the ulnar stem component is detachablycoupled to the proximal end of the ulnar stem component and the distallyextending portions of the humeral condyle portion. This modularity ofthe ulnar implant permits a common ulnar stem to be used with an ulnarbearing component that is either of a linked type or an unlinked type.

These and other aspects, features and advantages shall be apparent fromthe accompanying Drawings and description of certain embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

A few exemplary embodiments of the invention are depicted in thefollowing figures, in which:

FIG. 1 provides a perspective view of an illustrative modular, unlinkedelbow replacement device in accordance with some embodiments of thedisclosed subject matter,

FIG. 2 provides a perspective view of an illustrative modular, linkedelbow replacement device in accordance with some embodiments of thedisclosed subject matter,

FIG. 3A provides a perspective view of an illustrative non-modular,non-cemented humeral component in accordance with some embodiments ofthe disclosed subject matter,

FIG. 3B provides a perspective view of a non-modular, cemented humeralcomponent in accordance with some embodiments of the disclosed subjectmatter,

FIG. 3C provides a perspective view of a non-cemented humeral componentwith lateral recess in accordance with some embodiments of the disclosedsubject matter,

FIG. 4 provides perspective views of a non-cemented humeral sleeve inaccordance with some embodiments of the disclosed subject matter,

FIG. 5 provides a perspective view of a modular, humeral condylecomponent in accordance with some embodiments of the disclosed subjectmatter,

FIG. 6 provides a perspective view of an alternate non-cemented, modularhumeral stem design in accordance with some embodiments of the disclosedsubject matter,

FIG. 7 provides a perspective view of an articulation-adjustable ulnarcomponent in linked state in accordance with some embodiments of thedisclosed subject matter,

FIG. 8 provides a perspective view of an alternate, non-cemented ulnarstem design in accordance with some embodiments of the disclosed subjectmatter,

FIG. 9 provides a perspective view of an articulation-adjustable ulnarcomponent in unlinked state in accordance with some embodiments of thedisclosed subject matter,

FIG. 10 provides a perspective view of an ulnar stem and unlinked ulnarbearing in accordance with some embodiments of the disclosed subjectmatter,

FIG. 11 provides a perspective view of an ulnar stem, linked ulnarbearing, and linked ulnar bearing housing in accordance with someembodiments of the disclosed subject matter,

FIG. 12 illustrates differences in articular geometry between thehumeral condyles and ulnar bearing surfaces in accordance with someembodiments of the disclosed subject matter.

FIG. 13 illustrates a shift in contact point at articulation as externalmoment is applied in accordance with some embodiments of the disclosedsubject matter,

FIG. 14A illustrates differences in articular geometry of the humeralcondyles in accordance with some embodiments of the disclosed subjectmatter,

FIG. 14B illustrates differences in articular geometry of the ulnarbearing surfaces in accordance with some embodiments of the disclosedsubject matter,

FIG. 14C illustrates the articulation between the humeral and ulnarcomponents in accordance with some embodiments of the disclosed subjectmatter,

FIG. 15 provides perspective views of a bushing hole cap and bushings inaccordance with some embodiments of the disclosed subject matter,

FIG. 16 provides a sectional view of a humeral bushing and axle inaccordance with some embodiments of the disclosed subject matter,

FIG. 17 provides a sectional view of an elbow joint in varus-valgusstate in accordance with some embodiments of the disclosed subjectmatter,

FIG. 18 provides sectional views illustrating articulation of thebushing hole cap and bushings of FIG. 15 in accordance with someembodiments of the disclosed subject matter, and

FIG. 19 provides a perspective view of a radial head component inaccordance with some embodiments of the disclosed subject matter.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Apparatus and methods for total elbow replacement as described hereinallow a surgeon to intraoperatively select a linked or unlinkedconstraint by utilizing a connection located on the body of the ulnarand/or humeral stem. The elbow system can be either of a linked type orunliked type in that a humeral component can either be linked to anulnar component or they can be unlinked and free of attachment.Additional modularity also allows the selection of a cemented orcementless stem as described herein.

A modular total elbow replacement in accordance with some embodiments ofthe disclosed subject matter is shown in its unlinked and linkedversions in FIGS. 1 and 2, respectively.

Non-Modular, Non-Cemented Humeral Component Configuration

In some embodiments of the disclosed subject matter, the humeralcomponent 19 a may be non-modular and non-cemented as illustrated inFIG. 3A. In this geometry, the proximal stem 1 a is a curved cylinder.The proximal end of stem 1 a has a bullet shaped tip 1 b to improve thedistribution of load on the bone. The mid-portion geometry 1 c of thehumeral component 19 a curves anteriorly to approximately follow normalanatomy of the humerus. The mid-portion geometry 1 c has a posteriorconcavity 1 d that interacts with olecranon fossa and an anteriorconvexity 1 e creating a chevron-like cross-section, and is taperedmedial-laterally to transfer load to the humerus as distally aspossible. The outer surface of the mid-portion 1 c may be coated withplasma spray or porous metal and possibly hydroxyapatite to promotecementless fixation to bone. The distal end of the humeral component 19a has two extending bodies (medial 18 _(M) and lateral 18 _(L) condyles)that are separated by distance 13 as shown in FIG. 3B. In mostinstances, 18 _(M) will have a greater width (W_(Mh)) than 18 _(L)(W_(Lh)) (FIG. 14A), improving load transfer on the medial side. Themedial 18 _(M) and lateral 18 _(L) condyles have convex surfaces 21_(M,L) that contact corresponding concave unlinked ulnar bearing 5 a andlinked ulnar bearing 5 b. The contact is non-conforming. The condyles 18_(M,L) each have a cylindrical hole 17 that shares an axis 12 (theimplant joint axis) that may or may not be perpendicular to the longaxis of the proximal end of the humeral component 19 a.

The holes 17 accept either press-fit humeral bushings 3 b,c or bushinghole caps 3 a. The humeral component 19 can have a built-in carry angleα as shown in FIG. 3B. The humeral component 19 can have suture holes 16(FIGS. 3A and 3C) on the medial and lateral side for soft tissue/boneattachment. On the postero-lateral aspect of mid-portion geometry 1Cadjacent to condyle 18 _(L), there can be a recess 27 to contain anylateral bone fragments caused by an avulsion fracture for example. Therecess 27 will protect the fixation of said fragments from shear loadswhen used in conjunction with sutures which pass through suture holes16. It will be appreciated that plasma spray or porous coating aroundsuture holes 16, recess 27, and mid-portion geometry 1 c as seen inshaded regions in FIG. 3C will promote bone ingrowth.

Non-Modular, Cemented Humeral Component Configuration

In some embodiments of the disclosed subject matter, the humeralcomponent 19 b, as seen in FIG. 3B, can be cemented into bone. The shapeof the distal end of component 19 b can be identical to component 19 a.The shape of the cemented region of the humeral component 19 b can besimilar to embodiments shown in FIG. 3A but can be reduced in size tocreate room for cement (for example, ˜1 to 2 mm thick cement mantle),have a rectangular or triangular cross-section for rotational stability,and have radii 20 on respective corners to reduce stress in the bonecement. There is no porous coating on the cemented component.

Humeral Sleeve

In some embodiments of the disclosed subject matter, the mid-portiongeometry 1 c of the humeral component 19 a can be substituted with ahumeral sleeve 13, as illustrated in FIG. 4. The sleeve has an innergeometry 14 that mates with the body 10. The outer surface 15 of sleeve13 can be coated with plasma spray or porous metal and possiblyhydroxyapatite to promote cementless fixation to bone. The transverseouter cross-section of the sleeve 13 has a posterior concavity 13 a thatinteracts with olecranon fossa and an anterior convexity 13 b creating achevron to improve implant-bone contact, and is tapered medial-laterallyto transfer load to the humerus as distally as possible. The elbowreplacement system can include a number of humeral sleeves of differentgeometries such that the surgeon can select the sleeve most suited forthe patient's intramedullary anatomy. Sleeve 13 can have suture holes 16to allow a surgeon to pass sutures through the implant to attach softtissues to the implant, thus providing additional joint stability.Sleeve 13 can be used with modular or non-modular humeral component.

Modular Humeral Component Configuration

An alternative embodiment for a non-cemented and cemented humeralcomponent design is illustrated in FIG. 4 in accordance with someembodiments of the disclosed subject matter. The humeral condylecomponent 2 mates with humeral extending body 11 from the humeral stem1, thereby establishing modularity in both linked and unlinked elbowsystems. The distal end of the component 2 a has a geometry identical tothe distal end of humeral component 19 b as illustrated in FIG. 5. Theunlinked elbow system can also use a humeral condyle component 2 b whichis identical to component 2 a except that it does not have thecylindrical holes 17. Component 2 can have a built-in carry angle α.

The humeral condyle component 2 can have suture holes 16 (FIG. 3C) onthe medial and lateral side for soft tissue/bone attachment. On thepostero-lateral aspect of component 2 adjacent to condyle 18 _(L), therecan be a recess 27 to contain any lateral bone fragments. It will beappreciated that plasma spray or porous coating around suture holes 16,recess 27, and component 2 as seen in shaded regions in FIG. 3C willpromote bone ingrowth.

The elbow replacement system can have humeral condyle components 2 ofvarious geometries should the surgeon want to adjust the carrying angle,the constraint, and/or the condylar geometries. The humeral stem 1 canbe cementless as illustrated in FIG. 6, with a curved cylinder proximalstem 1 a, bullet tip 1 b, a mid-portion geometry 1 c that is plasmasprayed or porous coated, and a distal extending body 11 for engagementwith condyle component 2. Similarly, the mid-portion geometry 1 c can besubstituted with humeral sleeve 13, as illustrated in FIG. 4. Thehumeral stem 1 can also be cemented with a rectangular or triangularcross-section for rotational stability, and have radii on respectivecorners to reduce stress in the bone cement. In addition, the modularityat extending body 11 permits revision without the need to remove awell-fixed humeral stem 1 from the bone canal should, for example, thecondylar surfaces be worn or damaged.

The modularity of the humeral implant components thus permits a surgeonto interchange and match one humeral stem with one humeral condyleportion. Based on this feature, a hospital can predominantly stock onemodel of a humeral stem and a wider assortment of humeral condyleportions or vice versa. This allows greater savings by being able tostock less components as well as offering greater versatility as well asallow less components to be potentially used since an implanted stemremain in place while only the bearing component is replaced.

Articulation Adjustable Ulnar Component Configuration

As illustrated in FIGS. 7 and 8, a non-cemented, articulation-adjustableulnar stem 4 has a distal stem 4 b that is conical in shape andterminates with a bullet shaped tip 4 c to improve the distribution ofload on the bone. The mid-portion body 4 a has a medial/lateral andanterior/posterior and proximal/distal wedge and is approximatelypentagonal in cross-section 4 d where the apex interacts with thecoronoid process to provide rotational stability. The proximal body hasa large flat posterior surface 4 e to resist additional rotationalmoments about the stem axis. The proximal body 29 of ulnar stem 4 has asliding capture mechanism 28 that interacts with an unlinked ulnarbearing 5 a (FIG. 1) or a linked ulnar bearing housing 7 (FIG. 2)inserted from approximately a medial and/or lateral directionestablishing and adjustable articulation.

The capture mechanism 28 permits the selection of appropriately sizedcomponent, revision of worn components and/or facilitates conversionbetween unlinked and linked components as required. In the unlinkedstate as illustrated in FIG. 9, capture mechanism 28 interacts withengagement feature 33 (FIG. 10) on unlinked ulnar bearing 5 a. In thelinked state, capture mechanism 28 interacts with engagement feature 39on linked ulnar bearing housing 7 (FIG. 11).

As used herein, the term ulnar bearing component at least includes anulnar bearing that is configured to receive and engage the distallyextending portions (condyles) of the humeral condyle component. Asdescribed herein, the ulnar bearing component can be of an unlinked orlinked configuration. In the case of an unlinked configuration, theulnar bearing can directly engage the ulnar stem. In the case of alinked configuration, the ulnar bearing component can include anothermember (housing or substrate) that supports the ulnar bearing and isadapted to engage the ulnar stem.

Unlinked Ulnar Bearing Component

An unlinked ulnar bearing 5 a, as illustrated in FIG. 10, for example,has an engagement feature 33 that interacts with the sliding capturemechanism 28 of the ulnar stem 4 and that can be inserted fromapproximately the medial and/or lateral direction. The bearing 5 a canbe rigidly locked to the stem 4 using, for example, a locking component8. The unlinked ulnar bearing 5 a has two concave surfaces 31 _(M,L)that articulate with the convex humeral condyles 18 _(M,L). The medialsurface 31 _(M) may have a greater width (W_(Mu)) than lateral surface31 _(L) (W_(Lu)) (FIG. 14B), improving load transfer on the medial side.The articulation is non-conforming. The bearing 5 a also has a centralpost 30 that provides medial-lateral stability and a raised, distalarticular face 32 to resist posterior dislocation of the ulna in flexion(FIGS. 9 and 10). The post 30 may be rectangular or trapezoidal inshape. The articulation-adjustability of ulnar stem 4 allows a surgeonto select ulnar bearings 5 a of varying sizes/options defined by postthickness δ and/or bearing thickness γ for intra-operative adjustment ofthe degree of constraint, and/or various post alignments to adjust carryangle. The unlinked ulnar bearing 5 a may be made of a low frictionmaterial, for example, ultra-high molecular weight polyethylene(UHMWPE).

Linked Ulnar Bearing Component

A linked ulnar bearing housing 7, as illustrated in FIG. 11, has anengagement feature 39 that interacts with the sliding capture mechanism28 of the ulnar stem 4. The housing 7 has a central post 37 thatprovides medial-lateral stability of the linked elbow system. Thehousing 7 has a first opening 40 to accept a linked ulnar bearing 5 bfrom a medial and/or lateral direction. The linked ulnar bearing 5 b hastwo concave surfaces 41 _(M,L) that articulate with the convex humeralcondyles 18 _(M,L). The medial surface 41 _(M) may have a greater width(W_(Mu)) than lateral surface 41 _(L) (W_(Lu)) (FIG. 14B), improvingload transfer on the medial side. The articulation is non-conforming.The bearing 5 b can either be rigidly locked to central post 37 using,for example, a locking component 8, or act as a sliding platform withrespect to central post 37. Should the bearing 5 b need to be replaced,it can be removed from a medial or lateral direction. The linked ulnarbearing 5 b may be made of a low friction material, for example,ultra-high molecular weight polyethylene (UHMWPE). The elbow replacementsystem provides various housing options. The post thickness c and/orbearing thickness λ options permit intra-operative adjustment of thedegree of constraint. The post 37 has a second opening 38 for axle 6.The axle hole 38 location option allows the surgeon to adjustanterior-posterior η and/or superior-inferior ξ offset of the joint axis12. The axle 6 can be assembled from the medial and/or lateral directionto the central post 37 in vivo. The axle 6 can be rigidly locked tohousing 7 using, for example, a locking component 9. The central portion6 c of axle that mates with housing 7 can have a D-shaped cross-sectionto prevent rotation about the joint axis 12. The central portion 6 c mayhave a stop to prevent the central portion from advancing beyond centralpost 37. The ends 34 of the axle articulate with the inner diameters ofthe humeral bushings 3 b,c.

The cemented ulnar stem 4 f (FIG. 11) will have a similar shape to thenon-cemented ulnar component 4 (FIG. 8) proximally, but may have arectangular or triangular cross-section with rounded edges in the mid-4a and distal portion 4 b and be reduced in size to create room forcement (for example, ˜1 to 2 mm thick cement mantle).

Non-Confirming Articulation Between Humeral and Ulnar Bearing Components

The articulation between the humeral condyles 18 _(M,L) and ulnarbearings 5 a,b is not completely conforming in the sagittal plane(R_(3h)<R_(3u)) as illustrated in FIG. 12. The ratio of R_(3h)/R_(3u) isapproximately 0.95.

The articulation between the humeral condyles 18 _(M,L) and ulnarbearings 5 a,b in the coronal plane is not completely conforming as seenin FIGS. 13 and 14C. The humeral condyle articular surfaces 21 _(M,L)has a principal axis of rotation as defined by joint axis 12 as seen inFIGS. 14A,B,C. The articular surface 21 _(L) is created by revolving asingle radius R_(1HL) about axis 12 creating a convex surface. Thus, inone embodiment, the articular surface 21 _(L) and 21 _(M) can be definedby the same radius (i.e., R_(1HL)=R_(1HM)) (see FIG. 14A).

An alternative embodiment of articular surface 21 _(L), as illustratedin FIGS. 14A and 14C, similarly has a principal axis, but instead hastwo different radii R_(1HL) (near midline 12 a) and R_(2HL) (away frommidline 12 a) that tangentially meet at a distance β/2 away from midline12 a. Radii R_(1HL) and R_(2HL) are revolved around joint axis 12 tocreate a convex surface. In other words, the bearing surface (articularsurface 21 _(L), 21 _(m)) of each condyle 18 _(M,L) is defined by atleast two different radii. In the figures, radius R_(1HL) represents aninner (medial) radius of the lateral condyle 18 _(L), while radiusR_(2HL) represents an outer (lateral) radius of the lateral condyle 18_(L). Similarly, radius R_(1HM) represents an inner (medial) radius ofthe medial condyle 18 _(M), while radius R_(2HM) represents an outer(lateral) radius of the medial condyle 18 _(M). It will therefore thusbe appreciated that the radii of the condyles 18 _(M,L) at the center ofthe implant are different than the radii at the outer (lateral) edges ofthe respective condyles (lateral edges of the implant).

The medial-lateral width of condyles 18 _(M) and 18 _(L) are defined byW_(HM) and W_(HL), respectively. The medial articular surface 21 _(M)may not be equivalent to the lateral articular surface 21 _(L) when thefollowing conditions exist: radius R_(1HM) does not be equal to R_(1HL),radius R_(2HM) does not be equal to R_(2HL), and/or W_(HM) does notequal W_(HL).

The articular surface 31 _(L), 41 _(L) is created by revolving a singleradius R_(1UL) about axis 12 creating a concave surface (FIG. 14B).Thus, in one embodiment, the articular surface 31 _(L) and 31 _(M) (and41 _(L) and 41 _(M)) can be defined by the same radius (i.e.,R_(1UL)=R_(1UM)) (see FIG. 14B).

An alternative embodiment of articular surface 31 _(L), 41L, asillustrated in FIGS. 14B and 14C, has instead two different radiiR_(1UL) (near midline 12 a) and R_(2UL) (away from midline 12 a) thatare revolved around joint axis 12 to create a concave surface. In thefigures, radius R_(1UL) represents an inner (medial) radius of thelateral surface 31 _(L), 41 _(L), while radius R_(2UL) represents anouter (lateral) radius of the lateral surface 31 _(L), 41 _(L).Similarly, radius R_(1UM) represents an inner (medial) radius of themedial surface 31 _(M), 41 _(M), while radius R_(2UM) represents anouter (lateral) radius of the medial surface 31 _(M), 41 _(M). It willtherefore thus be appreciated that the radii of the surface 31 _(M,L)and 41 _(M,L) at the center of the implant are different than the radiiat the outer edges of the respective condyles (lateral edges of theimplant).

The medial-lateral width of surfaces 31 _(M) and 41 _(M) is defined byW_(UM). The medial-lateral width of surfaces 31 _(L) and 41 _(L) isdefined by W_(UL). The medial articular surfaces 31 _(M) and 41 _(M) maynot be equivalent to the lateral articular surfaces 31 _(M) and 41 _(M),respectively when the following conditions exist: radius R_(1UM) doesnot be equal to R_(1UL), radius R_(2UM) does not be equal to R_(2UL),and/or W_(UM) does not equal W_(UL). As the two radii humeral condyle 18embodiment pivots about respective two radii ulnar bearing surface 31,41with an applied external moment, as seen in FIGS. 13 and 14C, thecontact location on respective articulation shifts outwardly (away frommidline 12 a) thereby gradually increasing the restoring moment.

The articular surfaces 31 _(M,L) of unlinked ulnar bearing 5 a are verysimilar to articular surfaces 41 _(M,L). The unlinked bearing 5 a,however, has a raised distal face 32, as seen in FIG. 9, and extendsfurther superiorly than linked bearing 5 b. As a result, the concavityopens up at these extending regions to increase range of motion of theelbow joint.

Accordingly, the articulation between the humeral condyles 18 _(M,L) andulnar bearings 5 a,b in the coronal plane is not completely conformingas illustrated in FIGS. 13 and 14C. The ratios of R_(1HL)/R_(1UL),R_(1HM)/R_(1UM), R_(2HL)/R_(2UL), and R_(2HM)/R_(2UM) are approximately0.85-0.98.

It will be understood that the top arrow in FIG. 13 describes an appliedcompressive force (F) across the joint, and the 2 bottom arrows describethe joint reaction force (F/2). As a varus moment (M+) (represented bythe first curved arrow) is applied, the joint reaction force (F+)becomes greater on the medial side (longer bottom arrow) than thelateral side (shorter bottom arrow). As a greater varus moment (M++)(represented by the second curved arrow) is applied, the joint reactionforce (F++) is completely on the medial side creating lift-off on thelateral side. In addition, the contact location of joint reaction force(F++) and shifts outwardly distance X as R_(2HL) rolls onto R_(2UL) asindicated in the rightmost figure of FIG. 13.

Thus, in accordance with one embodiment of the present invention, thebearing surfaces of the humeral condyles 18 _(M,L) and ulnar bearings 5a,b are not toroidal in shape as in conventional designs but instead,each of the associated bearing surfaces has a cross-section in a coronalplane that exhibits at least two different radii. This constructionprovides for a shifting or migrating contact (in the lateral direction)between the two mating components during movement between the twocomponents and provides for the advantages described herein.

Humeral Bushings for Linked Configuration

The humeral bushing 3 b,c, as illustrated in FIGS. 15 and 16 to be usedin the linked total elbow configuration, has a cylindrical outerdiameter 24 that is press-fit into the inner diameter 17 of medial 18_(M) or lateral humeral 18 _(L) condyles. In one example, the innerdiameter can be conical 26 a to increase contact area when it contactsthe end 34 a of a conical-shaped axle 6 a. The cone angle of the conicalaxle 6 a is less than the cone angle of the inner diameter 26 a ofconical bushing 3 b. In another example, the articulation 36 between thebarrel-shaped bushing 3 c and the barrel-shaped axle 6 b isnon-conforming. This curved articulation allows for improved contactpressure at all ranges of motion where axle 6 b contacts bushing 3 c asillustrated in FIG. 17. The bushing's central face 25 articulates withpost 37 of the linked ulnar bearing housing during medial-lateraltranslation, as illustrated in FIG. 18. The bushing may be made of a lowfriction material, for example, ultra-high molecular weight polyethylene(UHMWPE).

Humeral Bushing Cap for Unlinked Configuration

The humeral bushing hole cap 3 a, as illustrated in FIG. 15, can beinserted into the cylindrical hole 17 of either the medial 18 _(M) orlateral 18 _(L) humeral condyle, and can be used in an unlinked totalelbow configuration. The central face 23 of the cap articulates with thepost 30 of the unlinked ulnar bearing 5 a during medial-lateraltranslation, as illustrated in FIG. 18. Should the elbow be converted toa linked configuration, the caps 3 a can be removed and discarded.

A radial head component 42, as illustrated in FIG. 19, has a proximalbody 43 that articulates with the capitellum. The component 42 has adistal stem 44 that follows the axis of the shaft of the radius. Thestem 44 is coated with plasma spray or porous metal and possiblyhydroxyapatite to promote cementless fixation to bone.

A preferred overall carrying angle of the elbow replacement device is10° where the ulna has 3° of carrying angle, and the humerus has 7°.

The range of motion of the device may be from 0-160° degrees of flexion.

The device can be imbedded with a material that resorbs over time inparallel with the time it takes for the native elbow soft tissuestructures to heal. As the native elbow strengthens during the healingprocess, the resorption of the material causes the joint of the elbowreplacement to become less stiff.

With regard to the unlinked design, the convex humeral condyles 18articulate with a concave unlinked ulnar bearing surface 31. Thearticulation-adjustable ulnar stem 4 is allows for ulnar bearing 5 aexchange if the component wears or if a different constraint type isneeded. The ulnar bearing 5 a can come in various thicknesses γ toprovide intra-operative adjustment of soft tissue constraint. The post37 can come in various thicknesses δ to provide intra-operativeadjustment of implant constraint. The ulnar bearing 5 a is assembled tothe ulnar stem 4 from approximately a medial and/or lateral direction inorder to preserve the triceps attachment to the proximal ulna. Shouldthe humeral component not have a modular condyle connection 19 a and 19b, the bushings holes 17 can be capped-off 3 a to allow the condyles 18and the bushing cap central face 23 to articulate with the unlinkedulnar bearing 5 a.

With regard to the linked design, each convex humeral component condyle18 has cylindrical holes 17 along the same axis that capture press-fithumeral bushings 3 b,c. The linked ulnar bearing housing 7 is assembledto ulnar stem 4 from approximately a medial and/or lateral direction bymeans of a sliding capture mechanism 28 to preserve the tricepsattachment to the proximal ulna. The linked, convex ulnar bearing 5 bengages with the ulnar bearing housing 7 and can be revised if, forexample, the bearing surface wears over time. The axle 6 rigidly locksto the ulnar bearing housing 7 using, for example, a locking component9. The humeral articular surfaces engage the ulnar articular surfaces insequence (FIGS. 17 and 18): 1. Upon varus/valgus rotation, the medialand/or lateral humeral condylar surfaces 21 _(M,L) articulate with themedial and/or lateral bearing surfaces 41 of the linked ulnar bearing,respectively. 2. With further rotation, lift-off of one humeral condylefrom one ulnar bearing surface occurs, and the axle 6 articulates withthe inner surfaces 26 of the humeral bushings 3 b,c. 3. Upon furtherrotation and medial-lateral translation, the central faces 25 of thehumeral bushings 3 b,c articulate with the post 37 of the linked ulnarbearing housing.

The surgical technique for implanting in a patient the elbow replacementdevice disclosed herein avoids taking down the triceps. A medial orlateral approach can be used to implant the device. The approach is notminimally invasive, but rather soft tissue preserving. The lateral softtissue structures are preserved. The distal humeral epicondyles can beretained. Resection of the radial head is optional.

While the invention has been described in connection with certainembodiments thereof, the invention is capable of being practiced inother forms and using other materials and structures. Accordingly, theinvention is defined by the recitations in the claims appended heretoand equivalents thereof.

1. An elbow prosthesis comprising: a humeral stem component having adistal end and a proximal end; a humeral condyle component having adistal end and a proximal end, the proximal end of the humeral condylecomponent being adapted to attachably engage the distal end of thehumeral stem component, the distal end of the humeral condyle componentincluding distally extending portions; an ulnar stem component having adistal end and a proximal end; and an ulnar bearing component beingadapted to attachably engage the proximal end of the ulnar stemcomponent and engage the distally extending portions of the humeralcondyle component.
 2. The elbow prosthesis of claim 1, wherein thedistal end of the humeral condyle component is formed of two distallyextending portions, each distally extending portion having a holeextending therethrough.
 3. The elbow prosthesis of claim 2, furthercomprising: a humeral bushing assembly that includes a pair of humeralbushings that are received within the holes of the distally extendingportions of the humeral condyle component; and an axle that passesthrough the humeral bushings and through an opening formed in the ulnarbearing component for detachably linking the humeral condyle componentto the ulnar bearing component.
 4. The elbow prosthesis of claim 3,wherein the axle is rigidly locked to a housing that part of the ulnarbearing component and is coupled to the ulnar stem component.
 5. Theelbow prosthesis of claim 3, wherein the axle includes a firstbarrel-shaped end portion and an opposite second barrel-shaped endportion with a central portion disposed therebetween.
 6. The elbowprosthesis of claim 5, wherein the first and second barrel-shaped endportions articulate with inner surfaces of the humeral bushings.
 7. Theelbow prosthesis of claim 2, wherein the holes of the distally extendingportion removably receive at least one of: (1) a pair of bushing holecaps when the humeral condyle component is in an unlinked orientationrelative to the ulnar bearing component; and (2) a pair of humeralbushing members that are configured to receive an axle that passesthrough the bushing members and through the ulnar bearing component whenthe humeral condyle component is in a linked orientation relative to theulnar bearing component.
 8. The elbow prosthesis of claim 1, wherein atleast one of the humeral stem component and the ulnar stem component hasa porous coating.
 9. The elbow prosthesis of claim 1, further comprisinga humeral sleeve component, the humeral sleeve component having an innergeometry configured to receive the humeral stem component to allow thehumeral sleeve to mate with the humeral stem with the humeral sleevesurrounding the humeral stem component.
 10. The elbow prosthesis ofclaim 9, wherein a transverse outer cross-section of the sleeve has aposterior concavity and an anterior convexity creating a chevron toimprove implant-bone contact.
 11. The elbow prosthesis of claim 1,wherein the ulnar stem component includes a structure at the proximalend of the ulnar stem component for engagement with the ulnar bearingcomponent to permit the ulnar bearing component to be detachably coupledto the ulnar stem component, thereby, allowing the ulnar bearingcomponent to be removed even when the ulnar stem component is fixedlyattached to the ulnar of a patient.
 12. (canceled)
 13. The elbowprosthesis of claim 1, wherein each distally extending portion has acontact bearing surface defined by a single radius as measured in acoronal plane.
 14. The elbow prosthesis of claim 1, wherein eachdistally extending portion has a contact bearing surface that has across-section in a coronal plane that exhibits at least two differentradii, the ulnar bearing component having complementary bearing surfacesthat mate with the contact bearing surfaces of the distally extendingportions, wherein each of the bearing surface of the ulnar bearingcomponent has a cross-section in a coronal plane that exhibits at leasttwo different radii.
 15. The elbow prosthesis of claim 1, wherein thebearing surfaces of the distally extending portions and the ulnarbearing component are configured such that varus and valgus rotation ofthe humeral condyle component relative to the ulnar bearing componentcauses a contact point between the humeral condyle component relative tothe ulnar bearing component to move outwardly.
 16. The elbow prosthesisof claim 14, wherein an inner radius of each of the bearing surfaces ofthe distally extending portions is less than an outer radius thereof.17. The elbow prosthesis of claim 1, wherein at least one of the humeralcondyle component and the humeral stem component has a cavity at one endfor receiving an extension formed at an end of the other of the humeralcondyle component and the humeral stem component to thereby establishingmodularity and permit the humeral condyle component to be removed evenwhen the humeral stem component is fixedly attached to the humeral ofthe patient.
 18. The elbow prosthesis of claim 1, wherein the humeralcondyle component includes at least one suture hole on at least one of amedial side and a lateral side thereof for soft tissue/bone attachmentand on an postero-lateral aspect of the humeral condyle componentadjacent to a lateral condyle thereof, a recess is formed to contain anylateral bone fragments.
 19. (canceled)
 20. (canceled)
 21. (canceled) 22.(canceled)
 23. (canceled)
 24. (canceled)
 25. (canceled)
 26. An elbowprosthesis comprising: a humeral implant having a stem and a humeralcondyle portion disposed at an end of the stem, the humeral condyleportion including distally extending portions; an ulnar stem componenthaving a distal end and a proximal end; and an ulnar bearing componentthat is a separate component relative to the ulnar stem component and isdetachably coupled to the proximal end of the ulnar stem component andengages the distally extending portions of the humeral condyle portion.27. The elbow prosthesis of claim 26, wherein the humeral implant is ofa modular type and the humeral condyle portion comprises a humeralcondyle component that is separate from the stem and is detachablyattached to the stem.
 28. The elbow prosthesis of claim 26, wherein theulnar bearing component is of a linked type relative to the humeralimplant and includes a housing that is detachably coupled to the ulnarstem component, wherein a link extends through openings formed in thedistally extending portions and through the housing for linking thehumeral condyle component to the ulnar bearing component.
 29. The elbowprosthesis of claim 28, wherein the housing includes a central post thatprovides medial-lateral stability of the linked elbow system and islocated between the distally extending portions of the humeral condylecomponent, the housing having a first opening to receive an ulnarbearing from at least one of a medial and lateral direction and a secondopening that receives the link, the ulnar bearing being a part of theulnar bearing component that engages the distally extending portions.30. The elbow prosthesis of claim 26, wherein the ulnar bearingcomponent is of an unlinked type relative to the humeral implant and theulnar bearing component is coupled to the ulnar stem component, whereinthe ulnar bearing component further includes a post that is disposedbetween the distally extending portions of the humeral condylecomponent.
 31. The elbow prosthesis of claim 26, wherein the distallyextending portions define condylar bearing surfaces, each condylarbearing surface and each bearing surface of the ulnar bearing componenthas a cross-section in a coronal plane that exhibits at least twodifferent radii such that varus or valgus rotation of the humeralcondyle component relative to the ulnar bearing component causes acontact point between the condyle bearing surface and the bearingsurfaces of the ulnar bearing component to move outwardly. 32.(canceled)